Known fine materials include pulverized coal, silica sand, lime powder, plastic pellets and cereals. Pulverized coal is supplied as a fuel into for example a blast furnace or a firing furnace for manufacturing lime. Therefore, operation of a blast furnace or a firing furnace requires measurement of the flow rate of the pulverized coal supplied into the blast furnace or the firing furnace for manufacturing lime.
As a method for continuously transporting the fine material such as the pulverized coal from a temporary storage facility such as a hopper to a destination facility such as a firing furnace, the following method is known, which comprises:
connecting an end of a transport pipe to a carrier gas source;
connecting the other end of said transport pipe to a destination facility;
blowing a carrier gas from said carrier gas source into said transport pipe so that the carrier gas flows from an end of the transport pipe toward the other end thereof;
continuously supplying a fine material contained in a temporary storage facility, in the middle of said transport pipe, into said transport pipe through which said carrier gas flows; and,
transporting said fine material supplied into said transport pipe to the destination facility by said carrier gas flowing through said transport pipe.
As one of the apparatuses for measuring the flow rate of the fine material flowing through the transport pipe as mentioned above, the following apparatus is known.
As shown in FIG. 1, an end of a transport pipe 1 is connected with an air source (not shown), and the air is supplied from the air source (not shown) into the transport pipe 1. In this figure, 2 is a hopper. The hopper 2 has a closed structure. The reference numeral 7 represents a service tank. The top of the service tank 7 is open from which a fine material 11 is supplied into the service tank 7 from time to time by an appropriate supply means. The lower exit of the service tank 7 air-tightly communicates with the upper entry of the hopper 2 by a first communication pipe 4. A first rotary valve 5 and a first expansion joint 6 are installed in the middle of the first communication pipe 4. In the open stateof the first rotary valve 5, therefore, the fine material 11 contained in the service tank 7 is supplied from the service tank 7 through the first communication pipe 4 into the hopper 2.
The lower exit of the hopper 2 air-tightly communicates with the transport pipe 1 by a second communication pipe 8. A second rotary valve 9 and a second expansion joint 10 are provided in the middle of the second communication pipe 8. The upper portion of the hopper 2 air-tightly communicates with the second communication pipe 8 by an equalizer 12. The pressure in the hopper 2 is kept substantially equal to that in the second communication pipe 8 through the equalizer 12. The fine material 11 contained in the hopper 2 is supplied through the second communication pipe 8 into the transport pipe 1, and transported by the air flowing through the transport pipe 1 to the other end of the transport pipe 1.
In FIG. 1, 3 is a load cell, attached to the hopper 2, for continuously measuring the weight of the fine material 11 contained in the hopper 2. The hopper 2 is supported through the load cell 3 on an appropriate supporting means (not shown).
The fine material 11 is continuously supplied from the hopper 2 through the second communication pipe 8 into the transport pipe 1 by controlling the first rotary valve 5 and the second rotary valve 9 as follows. The second rotary valve 9 is continuously open from the moment of starting transportation of the fine material 11, irrespective of whether the first rotary valve 5 is opened or closed. Therefore, the fine material 11 contained in the hopper 2 is continuously supplied through the second communication pipe 8 into the transport pipe 1. On the other hand,, an output signal of the load cell 3 is amplified by an amplifier 13, and fed into a differentiator 14 and a valve controller 15. In the valve controller 15, an upper limit value and a lower limit value of the weight of the fine material 11 contained in the hopper 2 are set up. Therefore, the fine material 11 contained in the service tank 7 is supplied into the hopper 2 through the first communication pipe 4, by continuously opening the first rotary valve 5 by the valve controller 15, until a measured value obtained by the load cell 3 reaches the upper limit value. Then, at the moment when a measured value obtained by the load cell 3 reaches the upper limit value, the first rotary valve 5 is closed by the valve controller 15. Subsequently, at the moment when a measured value obtained by the load cell 3 reaches the lower limit value, the first rotary valve 5 is opened by the valve controller 15, and the first rotary valve 5 is kept open by the valve controller 15 until a measured value obtained by the load cell 3 reaches the upper limit value.
The output signal of the load cell 3 fed to the differentiator 14 through the amplifier 13 is differentiated by the differentiator 14. An output signal of the differentiator 14 is fed through a differential value holder 16 to an appropriate recording or displaying means (not shown) as a calculating signal of the flow rate of the fine material 11 supplied from the hopper 2 into the transport pipe 1, while the first rotary valve 5 is closed. When the first rotary valve 5 is open, however, the fine material 11 is supplied from the service tank 7 through the first communication pipe 4 into the hopper 2. While the first rotary valve 5 is open, therefore, the load cell 3 cannot measure the weight of the fine material 11 supplied from the hopper 2 through the second communication pipe 8 into the transport pipe 1. Therefore, while the first rotary valve 5 is open, the differential value holder 16 holds a differential value of the output signal which is fed from the differentiator 14 at the time of the start of opening the first rotary valve 5, under the effect of the output signal of the valve controller 15, and feeds a signal having this differential value to an appropriate recording or displaying means (not shown) as a calculating signal of the flow rate of the fine material supplied from the hopper 2 through the second communication pipe 8 into the transport pipe 1.
Therefore, in the apparatus for measuring the flow rate of the fine material 11 flowing through the transport pipe 1 using the load cell 3 as mentioned above, it is impossible to accurately measure the flow rate of the fine material 11 flowing through the transport pipe 1 while the first rotary valve 5 is open.
In view of the above-mentioned inconveniences in the apparatus for measuring the flow rate of the fine material 11 flowing through the transport pipe 1 using the load cell 3, there has been proposed an apparatus for continuously measuring the flow rate of the fine material flowing through the transport pipe substantially identical with (1) an apparatus disclosed in Japanese patent publication No. 2,630/77 dated Jan. 2, 1977; (2) an apparatus disclosed in Japanese patent provisional publication No. 60,215/82 dated Apr. 12, 1982; and, (3) an apparatus disclosed in Japanese patent application No. 46,152/81 dated Mar. 31, 1981 which comprises:
a hopper having a closed structure;
a fine material feeding means, arranged above said hopper, for feeding said hopper with a fine material;
a weighing means for continuously measuring the weight of the fine material contained in said hopper;
a first communication pipe for air-tightly communicating said fine material feeding means and said hopper, said first communication pipe being adapted to introduce the fine material in said fine material feeding means into said hopper;
a first valve, provided in the middle of said first communication pipe, for opening and closing said first communication pipe;
a valve controller for controlling opening and closing of said first valve, said valve controller being adapted to control opening and closing of said first valve in response to a measured value obtained continuously by said weighing means so as to keep the weight of the fine material contained in said hopper within a prescribed range;
a transport pipe arranged below said hopper;
a second communication pipe for air-tightly communicating said hopper and said transport pipe, said second communication pipe being adapted to introduce the fine material in said hopper into said transport pipe;
a second valve, provided in the middle of said second communication pipe, for opening and closing said second communication pipe;
a carrier gas blowing means for blowing a carrier gas for transporting the fine material through said transport pipe into said transport pipe;
an equalizer for air-tightly communicating the top portion of said hopper and said second communication pipe, said equalizer being adapted to equalize the pressure in said hopper with the pressure in said second communication pipe;
a flow rate calculating means for calculating the flow rate of the fine material flowing through said transport pipe, said flow rate calculating means being adapted to continuously calculate the flow rate of the fine material flowing through said transport pipe, on the basis of the following item:
a measured value of the flow rate of the carrier gas flowing through said transport pipe, obtained by a flow rate measuring means, and a measured value of the pressure drop of a two-phase solid-gas flow which is flowing through said transport pipe, obtained by a pressure drop measuring means, said two-phase solid-gas flow comprising the fine material and the carrier gas, said pressure drop being measured between prescribed two points of the transport pipe in the axial direction thereof. PA1 m=G.sub.T /G.sub.a PA1 G.sub.s : flow rate of the fine material flowing through the transport pipe PA1 G.sub.a : flow rate of the carrier gas flowing through the transport pipe PA1 .alpha.=.DELTA.P.sub.T /.alpha.P.sub.a PA1 .DELTA.P.sub.T : pressure drop of the two-phase solid-gas flow which is flowing through the transport pipe between said prescribed two points of the transport pipe in the axial direction thereof PA1 .DELTA.P.sub.T =.DELTA.P.sub.s +.DELTA.P.sub.a PA1 .DELTA.P.sub.s : pressure drop caused by a flow of a fine material in the two-phase solid-gas flow which is flowing through the transport pipe, between said prescribed two points of the transport pipe in the axial direction thereof PA1 .DELTA.P.sub.a : Pressure drop caused by a flow of the carrier gas in the two-phase solid-gas flow which is flowing through the transport pipe, between said prescribed two points of the transport pipe in the axial direction thereof PA1 .DELTA.P.sub.a =C.sub.1 .multidot..gamma..multidot.U.sub.a.sup.2 PA1 U.sub.a : calculated value of flow velocity of the carrier gas flowing through the transport pipe PA1 U.sub.a =C.sub.2 .multidot.G.sub.a PA1 .gamma.: density of the carrier gas PA1 C.sub.1 : constant dependent on the measured values of the velocity and the density of the carrier gas flowing through the transport pipe in the absence of the fine material PA1 C.sub.2 : constant dependent on the shape of the transport pipe and the conditions of the carrier gas PA1 K: constant dependent on the shape of the transport pipe and physical properties of the fine material.
In the above-mentioned apparatus for continuously measuring the flow rate of the fine material flowing through a transport pipe, it is possible to continuously measure the flow rate of the fine material flowing through the transport pipe, without directly using the measured value obtained by the weighing means for measuring the weight of the fine material contained in the hopper. An example of the calculating operations in the above-mentioned apparatus is as follows:
Between two prescribed points of the transport pipe in the axial direction thereof through which the fine material and the carrier gas flow, the pressure drop ratio .alpha. and the mixing ratio m are expressed by the following equation: EQU m=k (.alpha.-1)
where,
By previously determining "K", "C.sub.1 " and "C.sub.2 ", "G.sub.s " can be calculated as follows: EQU G.sub.s =m.multidot.G.sub.a
However, in the above-mentioned apparatus for continuously measuring the flow rate of the fine material flowing through the transport pipe, the aforementioned constants "K", "C.sub.1 " and "C.sub.2 " vary with the wear of the inner surface of the transport pipe with time, and changes with time in particle size, moisture content, specific gravity, temperature and other physical properties of the fine material. This causes an error in the calculations performed for obtaining "G.sub.s ", thus making it impossible to accurately and continuously xeasure, over a long period of time, the flow rate of the fine material flowing through the transport pipe.